The present invention relates to a labeled protein and its producing method and a labeling compound to be used in the method. Also the present invention relates to a method for analyzing function of genes.
For labeling of protein expressed in cell-free translation systems and living cells is used generally a radiolabeling method that involves incorporating an amino acid labeled with a radioactive element such as .sup.35 S, .sup.3 H, .sup.14 C or the like into the translation product. However, amino acids may be used in reactions other than protein synthesis so that it happens that substances other than the translation product may be also labeled. On the other hand, the labeling method specific to the translation product includes the following method. To the .epsilon.-amino group of lysine, biotin is covalently linked, and the product is further linked through an ester linkage to tRNA having an anticodon for lysine to synthesize a complex (biotin-lysine-tRNA), which is put into a cell-free translation system to biotinate the translation product. The translation product is electrophoresed and then transferred on a membrane, and allowed to chemiluminesce with an alkali phosphatase by using a fusion protein of the alkaline phosphatase and streptoavidine. This chemiluminescence is recorded using X-ray film or the like for identifying the translation product (Promega, (1993) Technical Bulletin, No. 182, p.2). However, this method suffers from extreme instability of the synthesized biotin-lysine-tRNA (for 6 months at -70.degree. C.) and is expensive. Further, there is the problem that the procedure for identification is complicated and time-consuming. This is disadvantageous in automation for processing on a large scale. The translated protein is modified by biotin at a plurality of lysine side chains so that there is the possibility that its function and structure vary from the original one.